How about a simple card for warning indicators? I did a search and did not find anything easy.
The card would have a color choice to blink a couple of speeds and based on a boolean.
I would hate to make a helper boolean and automate it to blink on and off.
I appreciate any ideas I may have missed.
try using card mod and css
not simple 
but should net you create all sorts of warning effects
I tried an experiment and it worked a little. I will explain:
I downloaded a gif that said warning. Then I used the āConditional Card Configurationā.
pointed to the gif. problem is you have to make the gif live in your media folder on Home Assistant, navigate to it, copy the URL with itās certificate key. and use that in the card configuation.
Problem is; everytime you reboot āHASSIOā it creates a new key and you have to update the card with the new URL. OI!